1. Field of the Invention
This invention relates to an azimuth measuring apparatus for detecting an azimuth by means of earth magnetism and, more particularly, to a method for measuring an azimuth and an apparatus for measuring the azimuth which can accurately correct the detected azimuth.
2. Description of the Prior Art
An azimuth detector ior detecting an azimuth by means of earth magnetism is used, for example, in a navigation system carried on a vehicle.
This azimuth detector generally employs a flux gate sensor (i.e., "FGS") which outputs a signal corresponding to earth magnetism detected by two perpendicular coils. The azimuth is detected by combining the outputs of the coils.
A principle of detecting an azimuth will be described as follows. One of the coils first outputs a signal NS representing a north-to-south direction, and the other outputs a signal EW representing an east-to-west. When these output signals are combined by vectors, the trajectory of the end of the composite vector becomes a circle as designated in FIG. 10 when the measurements are ideally conducted. As shown in FIG. 10, the azimuth is obtained by the following equation. EQU .theta.=tan.sup.-1 ((EW output)/(NS output))
where .theta. indicates the angle from a magnetic north.
However, the above-described conventional azimuth measuring apparatus has the disadvantages that the trajectory of the composite vector does not become a true circle due to the error of the flux gate sensor and because the reliability of the measured azimuth is low.
For example, the NS signal becomes maximum or minimum and the EW signal becomes minimum or maximum in the vicinities of 0.degree., 90.degree., 180.degree. and 270.degree.. In this case, when the signal is converted to an angle near the maximum value according to an inverse trigonometric function, the error increases. Accordingly, when both the signals are combined, it is difficult to enhance the accuracy.
In the conventional apparatus, when the flux gate sensor is inclined or the earth magnetism is disordered, the apparatus has a further disadvantage that it cannot detect these conditions as an error.